What caused this space object’s weird orbit? ‘It was totally Planet Nine,’ one astronomer says.

Earlier this year, Konstantin Batygin, an astronomer at the California Institute of Technology, joined Ira Flatow on Science Fridayto discuss "Niku," the name for the newly discovered Kuiper Belt object with a wild orbit. (How wild, you ask? It moves at a 110-degree tilt to the rest of our solar system — backward.) Flatow asked whether the mysterious "Planet Nine" — which we haven’t located yet, and know little about — could have something to do with Niku’s strange orbit.

“I’m not saying it was Planet Nine, but between you and me, it was totally Planet Nine,” Batygin told Flatow.

And now, he can prove it. “I sort of joked around about it on the show, but then … I went downstairs, back to my office, and I thought, you know, this sounds of course like a long shot, but I might as well … do some numerical experiments,” he says.

Batygin ran the numbers with his collaborator Mike Brown. Even though Niku is currently too far away from Planet Nine to be affected by the massive planet’s gravitational influence, Batygin and Brown discovered a “dynamical pathway” that can explain Niku’s orbit, involving — you guessed it — the elusive Planet Nine.

“Through something called the 'Kozai-Lidov effect,' what Planet Nine does, is, it can take very distant orbits [and] twist them on their side, while they're still in the very distant parts of the solar system that are directly affected by Planet Nine’s gravity,” he says.

These distant, twisted orbits might intersect the orbit of Neptune. Batygin says that close encounters with Neptune can shrink the distant orbits and effectively pull them into the inner solar system. “So they get produced far away, and then they get shrunk and … frozen in these highly inclined, retrograde, very weird states.”  

Weird states like highly inclined, retrograde orbit of Niku — which Batygin and Brown were able to simulate in their experiments.

“We were like, ‘Wow, this actually generates not only Niku-type orbits, [but] we have one simulated particle that becomes, you know, truly an analog of this 110-degree tilted body,’” Batygin says. “And it’s quite remarkable.”

In this case, Batygin is confident that the proof of Planet Nine’s effects on Niku is all in the math. After all, the only ingredient in his numerical experiments is gravity, and there aren’t many surprises there.

“We know how that works pretty well in the solar system,” Batygin says, adding that "there's no question that such a pathway exists, provided the existence of Planet Nine.”

This article is based on an interview that aired on PRI's Science Friday.